const arrayEqual = function (arr1, arr2) { //判断两个数组是否相等
    if (arr1 === arr2) return true;
    if (arr1.length != arr2.length) return false;
    for (let i = 0; i < arr1.length; ++i) {
        if (arr1[i] !== arr2[i]) return false;
    }
    return true;
}